The present invention relates generally to compounds and methods for stabilizing soils, and more particularly to stabilizing agents and methods for application thereof which are effective in stabilizing finely divided soils such as clays and silts (hereinafter collectively referred to as "finely divided soils").
The construction of roadways, streets, parking lots, aircraft runways and the like of finely divided soils is difficult and expensive because of the inherent instability of such soils. The stabilization of soils with high organic content such as Chernozems, Andos, Brunizems, Podzols, alluvial and bog soils (hereinafter collectively referred to as "organic soils") also present a substantial problem. Some soils, of course, are a combination of both.
For many years a common approach to stabilizing such soil has been to incorporate "borrow" materials into the soil. Gravel and other granular materials, for example, have been commonly used in silts and clays with beneficial results. Crushed rock, because its angular characteristics provided both good support and good drainage, has been widely used as borrow material in all types of soils where it was economically available.
In addition to borrow materials, stability has been enhanced in finely divided soils by the use of line, cement and asphalt. In some cases, these compounds have been used to supplement the borrow materials because of their ability to modify the unstable characteristics of the soil. Cement has proven best in the silts and the very fine sands, while asphalt has been most effective in the coarser sands and for use with rock and gravel borrow materials. Lime has proven to be effective in stabilizing the true clays but unsatisfactory in silts and organic soils.
Lime-fly ash compositions have been utilized to improve the stability of borrow materials containing appreciable quantities of finely divided soils but have proven disappointing as a means of stabilizing true clays and silts, where no appreciable aggregate is present, and soils containing significant proportions of entrained organic residues.
Although all of these materials have helped resolve the difficult and expensive job of stabilizing finely divided soils and organic soils, in one way or another, each has its limitations and a considerable challenge still remains.
Borrow materials, for instance, are frequently not available without transport over great distances, which renders their use quite costly if not totally impractical. Cement and lime, used either alone as an additive to the native soil, or as a supplement to a grandular borrow materials, are expensive and difficult to apply in the quantities required. Asphalt is restricted in the more granular types of soil where it is helpful to stability and the lime-fly ash product is not helpful except where certain borrow materials are available.
It has long been evident that the chemistry of a soil has an important relationship to its stability characteristics and that chemically altering a soil can improve its stability. Prior to this disclosure, however, the economical and versatile manner provided has not been available.
The broad essence of the present invention resides in the discovery that applying to a finely divided soil, materials known to have a beneficial effect on the stability of such soils, and particularly a source of calcium (although magnesium or potassium can be quite effective in certain soils) with a reduction-oxidation stimulating compound such as sulfuric acid at concentrations of at least 45% by weight or a spent sulfuric acid, and substantial quantities of water (hereinafter referred to as "reaction product"), initiates rapid and substantial changes in the soil characteristics which greatly enhance its stability. Moreover, such changes can be accomplished even where the quantities of the chemicals applied and the methods of applying them are considerably less costly than the presently known stabilization approaches described above, and provide additional beneficial results including a significant reduction of the plasticity index and a substantial increase in the wet strength. By the addition of certain ancillary products to the reaction product of the invention, particularly certain chloride and sulfate compounds, it is also possible to substantially reduce, or even eliminate, shrinkage and swell of such soils and to reduce the plasticity index even further.
The soil stabilizing agent of the present invention combines certain of the properties of lime, or CaO, with some of those characteristic of asphalt, and at the same time functions as a reducing-oxidizing agent on organic matter in the soil. Because of chemical reactions initiated by the reducing-oxidizing agent, small quantities of calcium and other materials known to be beneficial to soil stabilization can be made to do a job which would require considerably greater quantities under the old approaches. The reaction product is quite compatible with asphaltic materials and can make those materials more effective as well. In sandy soils, the reaction product and asphalt make a particularly effective combination. Of course, my soil stabilizing agent can be effectively employed without asphaltic materials, and in some soil situations should be.
In solving soil stability problems, my reaction product is the key material, and, while by itself it does not materially reduce the shrinkage and swelling of expansive clays, when used in conjunction with certain ancillary products of the present invention it can accomplish this. These other products are essentially mixtures of sulfates in one case and mixtures of chlorides in another. For convenience, the ancillary products will be hereinafter referred to as the "sulfate product" and the "chloride product".
The reaction product is also highly compatible with naturally occurring carbonates. When properly applied, very high stability at low cost is achieved. At times, the use of the reaction product can do a job which is virtually impossible otherwise to accomplish. The use of the ancillary products of the present invention in conjunction with the reaction product can eliminate or rectify soft spots and frost damaged areas.
The following patents were cited against patent application Ser. No. 89,066, filed Nov. 12, 1970:
______________________________________ 2,705,681 Wishlinski Bituminous Composition and Process of Making It 2,833,663 Jenkins et al Method of Making Asphalt Emulsions 2,675,329 Schuessler Preparation of Metal Sulfonate Composition 243,167 Samman et al. Soil Stabilization (Australian) ______________________________________
These patents serve to characterize the prior art with which the present invention is clearly contrasted. Each requires a high pH and relies on saponification to achieve its purpose. The present invention requires a low pH, preferably below 2.0, does not involve saponification and achieves markedly superior results for its intended purposes, as will subsequently become apparent. The Brunel Pat. No. 3,400,006 cited against my allowed application Ser. No. 319,455, filed Dec. 29, 1972, relates to the addition of a lubricating oil acid sludge. As set forth later in this application, such sludges contain only about 30% H.sub.2 SO.sub.4 making them inadequate for the present invention. The Branksy Pat. No. 2,315,044, cited on allowance of Ser. No. 319,455, relates to the addition of sulfuric acid to an acid sludge product.